Abstract
Experiments in the system MgO-FeO-SiO2 have been the foundation of current beliefs that iron partitions preferentially into (Mg, Fe) O relative to the Mg-perovskite phase and occurs nearly all as Fe2+. Recent experiments in the system MgO-FeO-SiO2-Al2O3, however, show that (1) the presence of small amounts of Al stabilises Fe3+ in (Mg, Fe) SiO3 perovskite to values exceeding 50% Fe3+/·Fe; and (2) the solubility of Fe3+ in (Mg, Fe) O is extremely low at high P, T, regardless of oxygen fugacity. These results have important implications for physical and chemical properties of the lower mantle.
